The present invention relates generally to vacuum plasma processors using a coil and electrodes for establishing plasmas in a single processing chamber and, more particularly, to such a processor wherein the chamber includes a coil, a semiconductor electrode and a non-magnetic metal member arranged to prevent substantial electric field components the coil generates from being coupled to the semiconductor electrode. The invention also relates to a method of operating a vacuum plasma processor including a semiconductor electrode and a coil wherein fields derived from the electrode and coil establish plasmas with sufficient power to remove materials from a workpiece.
Vacuum plasma processors for processing workpieces, such as semiconductor wafers, dielectric plates and metal plates, frequently employ coils or electrodes to establish RF electromagnetic fields for exciting gases in vacuum processing chambers to an RF plasma. The coil excitation is frequently referred to as inductive, while the electrode excitation is frequently referred to as capacitive.
The capacitively and inductively coupled vacuum plasma processors are frequently employed to etch dielectric material from a semiconductor workpiece including an underlayer and a photoresist layer. The capacitive processors have an advantage over the inductive processors because the capacitive processors cause lower damage and have higher selectivity to the underlayer and photoresist layer. The inductive processors have an advantage over the capacitive processors because the inductive processors etch workpieces at a higher rate than the capacitive processors. The inductive processors have a higher oxygen dissociation rate to enable chambers to be cleaned more rapidly than can be attained by the capacitive processors.
Hybrid processors having both capacitive and inductive RF plasma excitation have been recently introduced to perform various etch applications in the capacitive mode and efficient photoresist stripping and chamber cleaning in the inductive mode. The hybrid processors can increase processing throughput and reduce processing costs because the same chamber can be used for multiple purposes without opening the chamber or moving the workpiece from chamber to chamber to perform different processes.
Collins et al., U.S. Pat. No. 6,077,384, and WO 97/08734 disclose prior art vacuum plasma processors including both inductive and capacitive coupling wherein a ceiling of a vacuum plasma processor chamber includes a high resistivity (e.g., 30 ohm-cm, i.e., a conductivity of 0.03 mho per cm, at room temperature) semiconductor window. The semiconductor window is between the processing chamber and an insulating structure carrying a flat or domed coil. The window extends from a central longitudinal axis of the chamber to a peripheral wall of the chamber. The semiconductor window must have hitch resistivity, i.e., low conductivity, to prevent substantial power dissipation in the semiconductor window. If the semiconductor window has a high conductivity, the electric field component of the coil electromagnetic field dissipates substantial power in the semiconductor so power necessary to achieve plasma ignition is not coupled to the gas. Collins et al. specifically states that if the semiconductor window has a high conductivity, such as a resistivity of 0.01 ohms-cms, i.e., a conductivity of 100 mhos/cm, the frequency of the RF induction field from the coil would have to be reduced to the kilohertz range or below to couple the field the coil generates through the semiconductor window.
Collins et al. discloses a grounded non-magnetic metal Faraday shield and or a powered or grounded non-magnetic metal backplane interposed between the semiconductor window and the coil. The non-magnetic metal backplane and Faraday shield include openings between turns of the coil and the semiconductor window so that the electric field component from the coil is coupled to the semiconductor window that extends continuously, in unbroken fashions, from the chamber center longitudinal axis to the chamber peripheral wall. The electric field components from the coil coupled through the Faraday shield and/or backplane have the same effect on the semiconductor window in the embodiments of FIGS. 25A and 37A of Collins et al. as in the embodiment of FIG. 1 of Collins et al., necessitating the use of a low conductivity semiconductor window in the embodiments of FIGS. 25A and 37A.
The semiconductor window, the backplane and Faraday shield are all made of non-magnetic material to couple the coil magnetic field components to the gas in the chamber to excite and/or maintain the gas in a plasma state. The non-magnetic metal backplane and Faraday shield openings in the backplane and Faraday shield reduce eddy current losses that occur in response to the magnetic field components.
The Collins et al. low conductivity semiconductor window has the disadvantage of applying a relatively low magnitude electromagnetic field to the plasma when the processor is operated in the capacitive mode. This is because the low conductivity silicon window does not have a high degree of electric field coupling to the plasma. Collins et al. state the semiconductor window is used for fluorine and polymerization scavenging from the plasma. The vast majority of the electromagnetic field etching which the Collins et al. device provides results from applying RF to an electrode on a chuck for the workpiece being processed.
It is, accordingly, an object of the present invention to provide a new and improved vacuum plasma processor apparatus and method for selectively, at different times, coupling plasma excitation electromagnetic fields derived from inductive and capacitive sources to gas in a single vacuum plasma processing chamber.
Another object of the invention is to provide a new, and improved vacuum plasma processor apparatus and method wherein a single vacuum plasma processing chamber can efficiently perform many different processing steps and can be cleaned without being opened.
A further object of the invention is to provide a the and improved vacuum plasma processor apparatus and method wherein a vacuum plasma processing chamber can be operated to provide relatively high processing throughput, to reduce the cost of workpiece fabrication.
An additional object of the invention is to provide a new and improved vacuum plasma processor apparatus and method wherein a vacuum plasma processing chamber can be selectively operated to enable workpieces to be processed (1) during certain time periods at relatively high speeds (2) at other times so workpiece damage is minimized, while providing high selectivity to underlayers and photoresist layers of wafers being processed.
Still another object of the invention is to provide a new and improved vacuum plasma processor including a chamber with a semiconductor plasma excitation electrode in close proximity to a plasma excitation coil, wherein the semiconductor electrode has a high enough conductivity to establish RF processing plasmas having sufficient field strength to process in particular, etch, workpieces in the chamber.
Yet another object of the invention is to provide a new and improved vacuum plasma processor with a chamber including inductive and capacitive plasma excitation, wherein a semiconductor electrode, having high enough conductivity to establish an electromagnetic field of sufficient strength to process and, in particular, to etch a workpiece, is in proximity to a coil, but does not interact with electric field components of the electromagnetic field the coil generates and which are coupled to gas in the chamber.
In accordance with one aspect of the invention, a vacuum plasma processor for processing workpieces comprises a vacuum chamber having an electrode arrangement including a semiconductor member, for ionizing gas in the chamber to a plasma. A coil outside the chamber generates an electromagnetic field for ionizing gas in the chamber to a plasma. A non-magnetic metal arrangement is interposed between the coil and the semiconductor member. The coil, non-magnetic metal arrangement and semiconductor member are positioned and arranged to prevent substantial electric field components of the electromagnetic field from being incident on the semiconductor member while enabling substantial electric and magnetic field components from the coil to be incident on the gas so the gas is ionized.
Another aspect of the invention relates to a vacuum plasma processor for processing workpieces that comprises a vacuum chamber having an electrode arrangement, including a semiconductor member, for ionizing gas in the chamber to a plasma. A coil outside the chamber generates an electromagnetic field for ionizing gas in the chamber to a plasma. A non-magnetic metal arrangement is interposed between the coil and the semiconductor member. The coil, non-magnetic metal arrangement and semiconductor member are positioned and arranged so (1) no portion of the semiconductor member is outside the interior of an inner turn of the coil, and (2) the non-magnetic metal arrangement includes a member having a periphery approximately aligned with the interior of the coil inner turn.
In first and second embodiments, the non-magnetic metal arrangement includes a member that is spaced from the semiconductor member and abuts the semiconductor member. In a third embodiment, the non-magnetic metal arrangement includes a first member abutting or adjacent the semiconductor member and a second member spaced from the semiconductor member.
The dielectric window, semiconductor member, and non-magnetic metal arrangement are preferably in a roof structure of the chamber. The coil has an interior portion that is spaced from a chamber center portion so peripheral portions of the semiconductor member are inside or approximately aligned with the coil interior portion. The non-magnetic metal arrangement has peripheral portions spaced from the chamber center portion by approximately the same distance as the semiconductor member peripheral portions. When the non-magnetic metal arrangement includes first and second members respectively abutting and spaced from the semiconductor member, the first non-magnetic metal member has a periphery slightly outside the periphery of the semiconductor member and the first and second non-magnetic metal members have approximately aligned peripheries.
In one preferred embodiment, particularly adapted for use with circular workpieces, e.g., semiconductor wafers, the chamber has a circular interior wall having a first diameter and the non-magnetic metal arrangement includes a member having a circular periphery having a second diameter, while the semiconductor member has a circular periphery having a third diameter. The chamber interior wall, the non-magnetic metal member and the semiconductor member are co-axial. The first diameter is greater than the second diameter, and the second diameter is approximately equal to the third diameter. The coil is substantially co-axial with the chamber interior wall and has a substantially circular innermost turn having a diameter approximately equal to the third diameter. When the non-magnetic metal member abuts or is adjacent the semiconductor member, the second diameter is slightly greater than the third diameter. When the non-magnetic metal member is adjacent the coil, it has a diameter slightly less than the interior diameter of the coil innermost turn. When the non-magnetic metal arrangement includes first and second circular members co-axial with the chamber interior wall and the first circular member abuts or is adjacent the semiconductor member and the second circular member is adjacent the coil, the second diameter is slightly greater than the third diameter and the second circular member has a diameter slightly less than the interior diameter of the coil innermost turn.
In the preferred embodiments, the semiconductor member is a flat plate while the non-magnetic metal member(s) can be flat plates or flat rings.
The semiconductor member has a high electric conductivity, e.g., no less than 0.01 mho/cm, and preferably at least 0.1 or 1.0 mho/cm so the semiconductor member can function as an efficient electrode to produce RF electromagnetic fields that supply sufficient power to the plasma to enable the plasma to remove materials from the workpiece.
A further aspect of the invention concerns a method of removing material from a workpiece in a vacuum plasma processing chamber including first and second spaced plasma excitation electrodes, one of which includes a semiconductor interposed between a plasma excitation coil and gas in the chamber, The method comprises removing the material during a first interval by energizing the coil so it supplies an RF ionizing electromagnetic field to the gas. The RF ionizing electromagnetic field has magnetic field components that are coupled through the semiconductor to the gas and electric field components that are coupled to the gas without being intercepted by the semiconductor. The electromagnetic field has sufficient power to cause a plasma resulting from the gas to be sufficiently energetic to etch the material. The material is removed during a second interval by energizing the electrodes so they supply an RF ionizing electromagnetic field to the gas. The RF ionizing electromagnetic field is coupled between the electrodes to the gas and material.
To maximize wafer processing throughout the chamber is preferably maintained in a vacuum state between the first and second intervals and the chamber is cleaned during a third interval by energizing the coil so it supplies an RF ionizing electromagnetic field to the gas. The electromagnetic field derived during the third interval has sufficient power to cause a plasma resulting from the gas to be sufficiently energetic to etch material deposited on interior surfaces of the chamber. The chamber is maintained in the vacuum state during the third interval, and between the first and third intervals, and between second and third intervals. The material can be a dielectric layer or a photoresist layer that is etched during the second internal or photoresist that is stripped from the workpiece during the first interval.